Marshall AVT 150 Valvestate

Disco Dave · 10-16-2009, 02:21 PM

Have replaced the output boards with tda chips but unfortunately the problem persists. Any ideas appreciated. I have a multimeter.Also if anyone has the schematic please send to ddjbarker@Hotmail.Com.

Disco Dave · 10-16-2009, 02:24 PM

Could it be the valve as there is no glow when power is on.

amptech · 10-22-2009, 11:44 PM

It must be a month of these!

had a whole heap of these of late with many different faults from total dead!
blow main fuse to dead front preamp stage's....

Had the pcb o/p stage solder tracks brunt away so end up moding the o/p stage via fitting a different and better power block made up from mosfet's and beefing up the 1000uf caps to 4700uf doe's the trick!
The ht supply to the 'o/p' ic is +- 47 volts so you can mod fit a block that will handle that plus give you near to rms power. mine gave 140w rms and still being hammer daliy

Even the mains tranformer was napped clean from the chassis!

The .22 ohm resistors at the preamps primary ac feed in was o/c so a quick replacement sorted that out and next broken pot's due to heavy drop abuse.

I nearly always see these units with the same old fault's burnt o/p stage so beefer o/p stage fit and your ready to jam

Jimmy74 · 11-04-2009, 01:43 PM

I'd be needing the schematic for the AVT150 too, please send to:

jimmy74@hotmail.it

thanks

Jazz P Bass · 11-04-2009, 02:55 PM

You might want to consider taking it to a reputable tech.
Just a thought.

10-22-2009, 11:44 PM	#38
amptech Member Join Date: Jun 2007 Location: SCOTLAND Posts: 69	avt 150 amps. It must be a month of these! had a whole heap of these of late with many different faults from total dead! blow main fuse to dead front preamp stage's.... Had the pcb o/p stage solder tracks brunt away so end up moding the o/p stage via fitting a different and better power block made up from mosfet's and beefing up the 1000uf caps to 4700uf doe's the trick! The ht supply to the 'o/p' ic is +- 47 volts so you can mod fit a block that will handle that plus give you near to rms power. mine gave 140w rms and still being hammer daliy Even the mains tranformer was napped clean from the chassis! The .22 ohm resistors at the preamps primary ac feed in was o/c so a quick replacement sorted that out and next broken pot's due to heavy drop abuse. I nearly always see these units with the same old fault's burnt o/p stage so beefer o/p stage fit and your ready to jam

11-04-2009, 02:55 PM	#40
Jazz P Bass Senior Member Join Date: Dec 2008 Location: Wernersville, PA Posts: 129	Tech help You might want to consider taking it to a reputable tech. Just a thought.

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10-16-2009, 02:21 PM	#36
Disco Dave Junior Member Join Date: Mar 2008 Location: Manchester, England Posts: 5	Have replaced the output boards with tda chips but unfortunately the problem persists. Any ideas appreciated. I have a multimeter.Also if anyone has the schematic please send to ddjbarker@Hotmail.Com.

10-16-2009, 02:24 PM	#37
Disco Dave Junior Member Join Date: Mar 2008 Location: Manchester, England Posts: 5	Could it be the valve as there is no glow when power is on.

11-04-2009, 01:43 PM	#39
Jimmy74 Junior Member Join Date: Mar 2009 Posts: 2	I'd be needing the schematic for the AVT150 too, please send to: jimmy74@hotmail.it thanks

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